This year is shaping up to be another big one for Transurban as the toll road group aims to sign off on the proposed $5.5 billion Western Distributor motorway in Melbourne and potentially bid for more roads in NSW and the United States.

While the company's stock price has slid over the past few months, from record highs of $12.65 in August to close at $10.38 on Friday as investors divert money away from infrastructure stocks into riskier assets, chief executive Scott Charlton's appetite for deals does not appear to be waning.

Over the next few months, the company expects to sign off on an "in principle" agreement with the Victorian government to build and operate the Western Distributor, which will widen Melbourne's West Gate Freeway and connect it to the Port of Melbourne, CityLink (which is already operated by Transurban) and the CBD via a new road tunnel.

Transurban has received initial bids from three consortiums of contractors keen to build the new Melbourne motorway, and expects to choose one before the Western Distributor's Environmental Effects statement is released midyear. Financial close of the project is not expected until the end of 2017.

Analysts have already started speculating where Transurban will get the cash from to pay for the Western Distributor, with Credit Suisse forecasting it will need to raise about $1 billion in equity.

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Transurban is reluctant to borrow too much for new projects, with the company aiming to keep its funds from operations to debt ratio – which measures a company's ability to use operating income to pay its debts – of between 8 and 12 per cent. The higher the ratio, the less risky the company is considered by credit ratings agencies.

Transurban has previously issued equity to help pay for its acquisitions of Queensland Motorway and Brisbane's Airportlink, with the equity raisings announced at the same time as the acquisitions.

The company will have more flexibility on the timing of any equity raising associated with the Western Distributor because it is a long-term development project not expected to be completed until 2022, requiring a more gradual influx of money. State and federal government contributions will cover about one-third of the motorway's costs.

Analysts at Moody's Investors Service have warned the Western Distributor will be a complex project for Transurban because it involves building both a tunnel and bridge. Moody's is monitoring whether the final agreement – which will include lengthening Transurban's concession on CityLInk for 10 or 12 years – will provide "an adequate buffer for managing the construction and traffic risk associated with the Western Distributor".

Transurban typically acquires the rights to operate toll roads after they are built and traffic flows are known, although it is also building a new toll road in Sydney, NorthConnex, which is expected to be finished in 2019.

But it may bid for concessions to manage parts of Sydney's new WestConnex toll road before the motorway's new tunnels open to traffic. Transurban, which has in-house traffic forecasters, is already positioning itself as a possible operator of WestConnex and has been having informal conversation with the NSW government, which has hired Goldman Sachs and law firm Ashurst to provide financing and sale advice.

However, the departure of NSW Premier Mike Baird, who is expected to be replaced on Monday by Treasurer Gladys Berejiklian, could affect a potential sale process of WestConnex if the new premier reviews the project. WestConnex has faced extensive protests in Sydney's inner-west, where homes have been destroyed to make way for the 33-kilometre toll road.

Credit Suisse has suggested that Transurban would have an advantage over other potential operators of WestConnex if the government sells off stages of the motorway before they open because its existing Sydney toll road network, which has benefited from a strong NSW economy, will help it forecast expected traffic flows. The M5 South-West toll road, already operated by Transurban, will connect directly with WestConnex.

However, other toll road operators, such as Spain's Cintra (owned by Ferrovial) and Abertis, are also expected to look closely at WestConnex, given it is a rare opportunity to get into the Australian toll road market, which is dominated by Transurban. Abertis lost out to Transurban in the sale of Queensland Motorways and Ferrovial's acquisition of Broadspectrum has given it a stronger foothold in Australia.

Any acquirers of WestConnex's early stages would have to take on the risk that its final stage – which involves more tunnelling to link the first and second stages – is delayed or does not eventuate. Credit Suisse has estimated that the final stage of the project has a "negative value" of $3.4 billion due to its high cost, which the NSW government has forecast at $7.2 billion.

Contractors have also warned the NSW government about pushing ahead too quickly with the final stage because they are already flat out working on several other big infrastructure projects in Sydney and Melbourne, putting pressure on resources and inflating wages and costs as they compete for engineers.

The Sydney Motorway Corporation is planning to release the proposed design for the third WestConnex stage for public consultation in January, followed by an environmental impact statement in mid-2017. It announced design changes in November to allow the third stage's tunnels to open earlier than expected in 2022.

In Brisbane, Transurban plans more unsolicited pitches to improve its Brisbane toll road network after securing a deal in November with the Queensland government to upgrade the Logan and Gateway Extension motorways.

Transurban, which owns 62.5 per cent of the 30-kilometre Logan motorway, will pay for the upgrade – which will double capacity at some interchanges – with existing debt facilities and will get returns on its investment by increasing toll fares for trucks.

Trucks will pay three times more than the fares paid by cars to use the motorways when the expansion is completed. (Trucks currently pay 2.65 times more than cars.)

Macquarie Infrastructure Partners is putting its stake up for sale. Macquarie Atlas has pre-emptive rights to buy out its partner, and is considering topping up its its share to 100 per cent. If it does get full control of Dulles Greenway, it could then sell all of the toll road on to Transurban, which wants to expand further in the US.

Transurban already owns and operates two motorways near Washington DC, 95 Express Lanes and 495 Express Lanes, and will this year start construction on a $US250 million project to extend the northern end of the 95 Express Lanes to the Washington DC border.

It is also keen to develop new toll road networks in other US regions. It lost a $4 billion tender in November to build new express lanes on Virginia's Interstate-66 highway to Ferrovial.

Meanwhile, the company also continues to explore how technological change will affect the evolution of roads and this year plans to run trials of driverless cars on Melbourne's CityLink road to see how they cope alongside cars with human drivers.